High-gain shock ignition is numerically investigated for specific marginally igniting targets?targets producing thermonuclear gain less than one?extracted from two distinct target families. Homothetic transformations keeping constant the implosion velocity, the adiabat, and the in-flight aspect ratio are used to draw target families. Conventional and fast ignition (FI) directly driven targets are considered for the Laser M?gajoule. It is shown that high gain can be achieved with shock ignition for designs, which do not ignite only from the laser compression. Shock ignition is achieved for different targets of the FI family, which are driven by an absorbed energy between 100? and 500?kJ and deliver thermonuclear energies between 10 and 130?MJ.

https://iopscience.iop.org/article/10.1088/1367-2630/12/4/043037/pdf

High-gain shock ignition of direct-drive ICF targets for the Laser Mégajoule

Peculiarities of the technique of the laser-induced film transfer (LIFT) are investigated. Possible mechanisms of tearing-off and transference of the films from the donor substrate (target) to the acceptor one are investigated. The main fields of LIFT applications are considered. One of the most interesting directions of LIFT applications—decontamination of radioactive surfaces—is investigated in detail. The main peculiarities and regimes of the processing are defined.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0263034606060289

Laser–induced film deposition by LIFT: Physical mechanisms and applications

A brief overview of the inertial fusion principles and schemes is presented. The bases for the laser driven ignition experiments programmed for the near future at the National Ignition Facility are outlined. These experiments adopt indirect-drive and aim at central ignition. The principles of alternate approaches, based on direct-drive and different routes to ignition (fast ignition and shock ignition) are also discussed. Gain curves are compared and discussed.

http://iopscience.iop.org/article/10.1088/0741-3335/51/12/124029/pdf

Laser driven inertial fusion: the physical basis of current and recently proposed ignition experiments

An arbitrary beam shaping-zooming concept is proposed for direct drive fusion on the Laser Megajoule and the National Ignition Facility. It is based on the intrinsic conception of these facilities which use four beamlets per beam. A substantial improvement of the laser–target coupling efficiency is achieved with a lowering of ignition threshold. A design providing a thermonuclear energy of about 30 MJ with less than 1 MJ energy-laser has been investigated. The control of low-modes irradiation uniformity is achieved dynamically with an enhancement of the hydrodynamic stability of the acceleration and deceleration phases.

https://iopscience.iop.org/article/10.1088/0029-5515/45/12/L01/pdf

Optimization of laser-target coupling efficiency for direct drive laser fusion

In the context of the French Laser-Mfusion-research programme, a direct-drive target design is developed. It is based on the use of a CH-foam ablator filled with cryogenic deuterium-tritium. One-dimensional optimization leads to a potential gain of 60 with a 1.5 MJ laser. The hydrodynamic stability of the implosion is investigated at the ablation front and the hot-spot surface by means of modelling and two-dimensional simulations. The effect of irradiation non-uniformities on low-mode (time-dependent) implosion asymmetries is studied by two-dimensional hydrodynamics simulations with three-dimensional laser-light raytracing. The effect of beam focal shapes on hot spot low-mode asymmetries is also addressed. PACS numbers: 52.273Bc

http://iopscience.iop.org/article/10.1088/0029-5515/44/10/005/pdf

High-gain direct-drive target design for the Laser Mégajoule

In the context of the French Laser Megajoule (LMJ) fusion research program, direct drive is an alternate to indirect drive to reach ignition and thermonuclear burn. We present recent progress in the direct-drive fusion studies for LMJ. Calculations have shown that the LMJ irradiation uniformity is characterized by long wavelength asymmetries compatible with direct drive requirements. Calculations of the irradiation uniformity in the context of indirect drive beam positioning have been done. We show that non-uniformity can be minimized by repointing the beams. Unfortunately, a time analysis shows that this nonuniformity increases strongly in time above levels usually considered inconsistent for direct drive. Finally, a recent baseline target design is presented and consists of a DT ice shell surrounded by a low-density CH foam wicked with cryogenic DT. This design can potentially reach a gain of 90 with a 1-MJ on-target laser driver. Hydrodynamic stability is increased at the ablation front and the laser–target coupling efficiency achieves 85%.

Progress in direct-drive fusion studies for the Laser Mégajoule

Foams are an important component of various inertial confinement fusion target schemes. The propagation of shock waves in foams is also an important issue for many other laser experiments (e.g., laboratory astrophysics experiments). The usual approach is to assume that the foam can be considered as a homogeneous mixture. Taking into account the effects of foam heterogeneity leads to increased shock velocity and reduced compressibility. Evidence of this effect is obtained using two-dimensional adaptive mesh refinement Eulerian numerical simulations. Nonetheless, for the very low density foams filled with DT ice used in recent direct drive target designs, the homogeneous mixture model provides adequate shock timing, density, and pressure profiles.

F. Garaude

Papers

High-gain direct-drive target design for the Laser Mégajoule

Progress in direct-drive fusion studies for the Laser Mégajoule

Effects of microstructure on shock propagation in foams